This document discusses the concept of pressure and provides examples. Pressure is defined as force per unit area, with the standard SI unit being the pascal (Pa). Higher pressures are caused by large forces applied over small areas, while lower pressures result from smaller forces applied over large areas. Examples are given of applications requiring high pressure, like nails, and low pressure, like caterpillar tracks. The document also provides a formula for calculating pressure and works through examples of determining pressure exerted by human feet on the ground.

1. Pressure
Modify : Chaiporn Pattanajak
Banphue pittayasan School
Udonthani
Thailand

2. Is a pushing force

3. Pressure is when a push, squashes
something
Walking pushes on the ground, if the
ground is soft it gets squashed and we
leave footprints

4. If the ground is very soft
we leave deep footprints

5. We can make less deep
footprints by spreading out
our weight (push) with special
shoes.

6. Which shoes do you think will
push hardest on the floor?

7. Sensible shoes?
• The force of our body pushing
down will exert a pressure
• The surface area of our shoes
in contact with the ground will
affect the pressure
• These stiletto shoes will
concentrate the force over a
small area
• These shoes will give a larger
pressure and would not be
suitable for walking on soft
ground

8. More sensible shoes
• These boots have a large surface
area
• The weight of a person is spread
out over the larger surface
• The pressure exerted by the person
is smaller than if they were
wearing stiletto shoes
• A small pressure means you will
not sink into soft ground

9. Examples of where a large area
is needed to reduce pressure.
Caterpillar tracks on diggers
and on tanks
Tyres on a tractor
Skis and snowboards
snowshoes

10. Examples of where a small area is
needed to increase the pressure
• Nails
• Needles
• Kitchen knives
• Scissors
• Drawing pins
• Spade

11. Questions on pressure
1) What combination of force
and area give a high
pressure?
2) What combination of force
and area give a low
pressure?
3) What is the formula for
calculating pressure?
4) What units are pressure
given in?
Answers:
1) Large force and
small area
2) Small force on
large area
3) Pressure =
force /area
4) Pascals (Pa)

12. Press
urePressure is define as force
per unit area, where the
force F is understood to be
the magnitude of force
acting perpendicular to the
surface area A.: The SI unit of
pressure is N/m2
.This unit has the official
name Pascal(Pa).1 Pa = 1
A
F
P =
Area
F

13. Example 10-2
• Calculating pressure. The two feet of a 60-
kg person cover an area of 500 cm2
. (a)
Determine the pressure exerted by two the
feet on the ground. (b) If the person stands on
one foot, what will the pressure be under that
foot?
• Approach. Assume the person is at rest.
Then the ground pushed up on her with a
force equal to her weight mg, and exerts a
force mg on the ground where her feet (or
foot) contract it.
• Because 1 cm2
= (10-2
m)2
= 10-4
m2

14. (a) The pressure on the
ground exerted by the
two feet is 23
2
2
/102.1
05.0
)/10()60(
mNx
m
smxkg
A
mg
A
F
P ====
(b) If the person stands on
one foot, the force is still
equal to the person's
weight, but the area will be
half as so much, so the
pressure will be twice as
=
2.4x103
N/m2

15. Practice using the formula for pressure
1. A box weighs 500N. It’s base
has an area of 5 m2
. What
pressure does it exert?
2. Another identical box is placed
on top of the first box. What
is the pressure now?
3. A snowboarder weighs 600N.
The area of the snowboard is
0.5m2
. What is the pressure
on the snow?
Answers:
1. 100 Pa
2. 200 Pa